1. Field of the Invention
The present invention relates to an ink jet recording apparatus and recovery method for a recording head, in which the recording is performed by discharging the ink onto a recording medium.
2. Related Background Art
A recording apparatus for printer, copying machine and facsimile terminal equipment is constituted to record images constructed of dot patterns onto a recording medium such as paper or plastic sheet, based on the image information.
The recording apparatus as above mentioned can be classified into the printing methods of ink jet, wire dot-matrix, thermal, and laser beam. Among them, the ink jet printing (ink jet recording apparatus) is constituted to discharge fine droplets or mists of recording liquid (ink) through discharge ports of an ink jet recording head, and to deposit them onto recording medium.
This ink jet recording apparatus has many advantages, for example, high-speed printing, and easy full colored printing.
To exhibit this advantage sufficiently for a long term, a recovery operation can be performed to prevent or resolve clogging of discharge ports beforehand, or remove impurities such as dirt that enters into the head. A conventional recovery operation will be described below.
FIG. 1 is a typical view showing an example of the ink supply system in the recovery operation for a recording head of conventional ink jet recording apparatus.
In FIG. 1, a storage tank 6 for storing ink and a common liquid chamber 2 for the recording head are connected via a first flow channel 11 and a second flow channel 12. A recovery pump 9 for circulating the ink is connected to one of the flow channels (first channel 1 in the example as shown in the figure), in order to exhaust bubbles in each flow channel or thickened ink in discharge ports (liquid channels).
The flow channels 11, 12 are provided with filters 16, 16, respectively, to capture contaminants. Note that the filters 16, 16 are more effective if they are located closer to a discharge section (for example, liquid channels leading to discharge ports), and in the example as shown in the figure, they are provided at the junctions with each of the flow channels 11, 12 in the common liquid chamber 2.
As above described, a method in which the ink is supplied from one end portion of the common liquid chamber 2 by the recovery pump 9, and circulated from the other end portion of the common liquid chamber 2 into the storage tank 6 is effective to remove bubbles in the flow channels 11, 12 and within the common liquid chamber 2, and more effective particularly when the full-line recording head having a number of discharge ports 3 is used.
In such ink supply system, as the flow channel resistance in the recovery pump 9 is large during the recording operation, the ink flows from the storage tank 6 through the second flow channel 12 into the recording head 1.
FIG. 2 is a typical view showing another example of the ink supply system in a conventional ink jet recording apparatus.
In this example, a recording tank 5 is provided as another storage tank, in addition to a main tank 6, in which if the ink within the recording tank 5 falls below a predetermined quantity, the ink is refilled from the storage tank 6 by a recovery pump 9.
Other ink flows are the same as those in the previously-mentioned ink supply system (FIG. 1), except that in this example, a solenoid valve 7 is provided in a second flow channel, and the ink in a first flow channel 11 and within the common liquid chamber 2 can be exhausted through discharge ports without being returned to the storage tank (recording tank), by activating the recovery pump 9 with the solenoid valve 7 closed. And in this example, filters 14, 14 are provided midway of the first and second flow channels.
Further, a straightening valve 8 for refilling and a straightening valve 10 for recovery are connected at the positions as indicated of the first flow channel 11.
Note that numeral 4 indicates a discharge port face where the discharge ports 3 of the recording head 1 are arranged, and numeral 13 indicates an air vent valve for the storage tank (recording tank).
In a conventional ink supply system as above described, the ink flows through the first flow channel 11 to the recording head 1 during the recovery operation, while it flows through the second flow channel 12 to the recording head 1 during the recording operation, and thus filters 16, 16 or 14, 14 are needed in both flow channels.
However, there is a possibility that discharge failure may occur due to clogging in the liquid channels leading to the discharge ports 3, because fine contaminants passing through the above-mentioned filter have got entangled within the common liquid chamber 2 and may amass and not pass through the filter, or materials peeled off from the interior of the common liquid chamber or contaminants enclosed into the common liquid chamber 2 at the manufacturing process, are caught between two filter plates and can not move from the vicinity of the common liquid chamber 2.
If the discharge ports 3 are more densified, the mesh of the above-mentioned filter must be made more finely, in which the area of filter is required to be larger to prevent the loss of pressure. Specifically, in the first constitutional example (FIG. 1), there was a problem that the recording head containing the above-mentioned filters must be constructed more largely.
Further, FIG. 3 is a typical view showing another example of the ink supply system to a recording head of a conventional ink jet recording apparatus.
In FIG. 3, a recording head (ink jet recording head) 101 is provided with an ink liquid chamber 114 capable of storing ink, and discharge ports 110 for discharging the ink flowing in from the ink liquid chamber, wherein the discharge ports 110 and the ink liquid chamber 114 are communicated via liquid channels where discharge energy generating elements (electricity-heat converters such as heat generating elements) are disposed.
A main tank 102 for storing ink and the ink liquid chamber 114 in the recording head 101 are connected via a first ink flow channel 116A and a second ink flow channel 116B. And a recovery pump 103 is connected to one of the flow channels (first flow channel 116A in the example as shown) in order to exhaust bubbles within the recording head 101 or in the flow channels 116A, 116B, or thickened ink within discharge ports (liquid channels) by feeding ink into the recording head 101.
The flow channels 116A, 116B are provided with filters 117, 117, respectively, to capture contaminants.
As above described, a method in which the ink is supplied from one end portion of the ink liquid chamber 114 by the recovery pump 103, and circulated from the other end portion of the ink liquid chamber 114 into the main tank 102 is effective to remove bubbles in the ink channels 116A, 16B and within the ink liquid chamber 114, and more effective particularly when the full-line recording head having a number of discharge ports 3 is used.
In such ink supply system, as the liquid channel resistance in the recovery pump 103 is large during the recording operation, the ink flows from the main tank 102 through the second flow channel 116B into the recording head 101.
When the ink is circulated into the ink liquid chamber 114 by activating the above-mentioned recovery pump 103, the recovery function of the liquid channels or discharge ports 110 is effected by exhausting a partial quantity of ink from discharge ports 110 and removing cloggings produced therein together with bubbles as previously described.
Thus a cap 104 for receiving ink from discharge ports 110 is provided on the side opposed to the recording head 101, and in which it faces the recording head 101.
The ink exhausted into the cap 104 is passed through a waste ink flow channel 105 into a waste ink tank 106.
FIG. 4 is a typical view showing still another example of the ink supply system in a conventional ink jet recording apparatus.
In this constitutional example, a recording liquid supply tank 120 is provided in addition to a main tank 102, in which if the ink within the recording liquid supply tank 120 falls below a predetermined quantity, the ink is refilled from the main tank 102 through a straightening valve 123 for refilling by a recovery pump 103.
Other ink flows are the same as those in the previously-mentioned ink supply system (FIG. 3), except that in this constitutional example, a straightening valve 122 for recovery is provided in a first ink flow channel 116A, and a solenoid valve 119 is provided in a second ink flow channel 116B.
The ink supply system as shown in FIG. 4 is similar to that shown in FIG. 3 in the above-mentioned constitution, but other portions are constituted substantially in the same way.
In this constitutional example, the ink in the first ink flow channel 116A and within the ink liquid chamber 114 can be exhausted through discharge ports 110 without being returned to the recording liquid supply tank 120, by activating the recovery pump 103 with the solenoid valve 119 closed.
As in FIG. 3, a cap 104 for receiving ink exhausted from discharge ports 110 is provided on the side opposed to the recording head 101, and in which it faces the recording head 101 as shown.
The ink exhausted into the cap 104 is passed through a waste ink flow channel 105 into a waste ink tank 106. Note that numeral 121 indicates an air vent valve for the recording liquid supply tank 20.
FIG. 5 is a typical cross-sectional view showing the details for a portion of the recording head 101 and the cap 104 in the conventional ink supply system as shown in FIGS. 3 and 4.
The recording head 101 comprises an ink liquid chamber 114, a plurality of liquid channels 112 communicating to the ink liquid chamber 114, a plurality of discharge ports 110 formed at tip openings of liquid channels, and electricity-heat converters such as heat generating elements each of which is disposed in each of the liquid channels.
The electricity-heat converters 111 are discharge energy generating elements for generating the heat energy for use in discharging the ink, arranged in parallel one in each of liquid channels 112.
Thus, by driving the electricity-heat converters 111 in accordance with record data, an ink jet recording head 101 for discharging the ink through the discharge ports 110 can be constituted.
In the ink jet recording head 101, if recording failure occurs due to bubbles present on the liquid channels 112 as indicated by a in FIG. 5, or discharge failure occurs due to thickened ink remaining on tip portion of the liquid channels 112 when not used for a long period, bubbles or thickened ink can be exhausted through discharge ports 110 by activating the recovery pump 103. Waste ink exhausted is received into the cap 104 as previously described, and further passed into the waste ink tank 106.
A previously described, in the conventional ink jet recording apparatus, bubbles or thickened ink in the liquid channels 112 are exhausted by activating the recovery pump 103 to apply the pressure to the liquid channels 112 within the recording head 101 and circulate the ink.
In this case, however, if contaminants exist in the vicinity of communicating sections with the ink liquid chamber 114 as indicated by b in FIG. 5, there is a possibility that the contaminants are forced into liquid channels 112 with the applied ink pressure.
If the contaminants are forced into liquid channels 112, the ink can not flow smoothly into the liquid channels 112, thereby causing a recording failure.